Oversized DHCP option issues

[蒋圩淏]

Hello everyone,

I'm configuring a DHCP server over a network that has multiple
gateways. One of the gateways has limited bandwidth, so I'm thinking
of using the classless static route defined in RFC3442 to
automatically configure it.

However, our routing tables are large, exceeding the DHCP 255 bytes
limit. I observed that only packets within 255 bytes can be sent out
successfully while exceeding the limit by a little bit will cause a
malformed DHCP packet shown in Wireshark, and the DHCP server doesn't
send out the option while using the whole table.

In RFC3396 it specifies that the options should be concatenated when
they exceeded the 255-byte limit, while I didn't find how to configure
that in `dhcpd.conf`.

I've tried to add multiple options that share the same DHCP code, and
dhcpd just ignore the previous settings and only takes the last one.

The question is, how can I send out the large table successfully? I
think this problem could be practical, as the 255-byte option limit
can only store 23 CIDR-255.255.255.0 table entries.

--
Weihao Jiang
mailto:weihau.chiang at gmail.com
mailto:weihao.jiang at sjtu.edu.cn